Avid BB7 issues

Danny523

Hello!

So I just fitted a pair of avid bb7's to my bike, along with these cables http://www.chainreactioncycles.com/shim ... -prod14120

First of all they are really terrible at the moment, they will no way lock the wheels up at all. I know they need bedding in, but is it normal for them to be this bad?

Also will those cables be good enough? I was told afterwards that I need better cables than these? The do feel very spongy.

Thirdly I cant seem to get the disc aligned between the pads. I followed the instructions exactly and repeated over and over to try, but the disc seems slightly warped, If I look down through the gap between the pads I can see the disc "wobbling" as the wheel spins. Only slightly but its enough to keep touching the pad and making a noise.

Any advice would be greatly appreciated!

Thanks

Daniel

cooldad

Cables are fine, nothing at all wrong with Shimano stuff.
Setup, or rotor if it's warped.

Danny523

Could the rotors be warped straight out the box? I mean they are not 100% true, either of them. I can see that as they turn, is that not normal? You can't tell that they are until they spin, its very slight.

The Rookie

Yes they could be warped out the box, or the mounting on the wheel be not flat (or you have trapped debris) or them not bolted up right.

They should be adjusted on BOTH pads (seperately) so they 'just' rub, too much clearance and you'll never get good braking.

cobba

Danny523 wrote:

Could the rotors be warped straight out the box? I mean they are not 100% true, either of them.

Yes they can be slightly out of true

Pads will need to be 'broken in'.

Rotor truing:
http://www.youtube.com/watch?v=0fosSuyiCDE

BB7 Installation & Setup Guide:
http://cdn.sram.com/sites/default/files/techdocs/2006_BB5and7_English.pdf

Ouija

You can straighten the rotors up with a set of pliers. Just find and mark the section that's warped and bend it the opposite way with a pair the pliers but don't get carried away.

The closer the static pad gets to the rotor the better the breaking.

It's also worth noting that HOW you put the rotor on the hub can affect straightness. You should always tighten up three alternate screws very gently then do the other three rather than just go round all the screws, tightening them up in sequence (why is a little complicated to explain).

When centering the caliper, tighten both pads until it's clamped on the rotor and then gently tighten both bolts incrementally. In other words, don't just screw in the upper bolt until it's tight and then do the other one. Instead, apply a small amount of pressure to one, switch to the other and do the same and then go back to the first one etc, etc, etc. Failure to do this means the caliper will twist slightly when you tighten the bolts so that when you back the pads off they are no longer properly faced with the rotor and need to be backed off further away than is desirable.

Oh! And shimano cable work ok but they are a bit spongy. Any cable that acts like a spring (that if you bend it and let go it springs back to being straight again) is compressable. Jagwire cables are very rigid (you could club baby seals with them) and tend to give snappier performance on my BB7's. Also depends on how straight you do the cables. Too many kinks and curves and you lose some braking perfomance in the cables simply snapping straight (look at the cables as you pull the lever and see if the cables look like they are 'twitching').

You also lose some breaking performance by simply trying to bend the rigid rotor into the static pad which is why it's better to get that static pad as close to the rotor as possible, which is hard to do if the rotors bent and the calipers not properly aligned for the reasons mentioned above.

The Rookie

An adjustable spanner is better than pliers for straightening discs, no teeth to leave marks!

Danny523

Thank you so much everybody! Ill have a go and truing the rotors tomorrow. Ill maybe see about replacing the cables after a few rides and see how they feel.
I took it out for a quick ride today and the brakes are already feeling more powerful.

Thanks again!

r3hxn

how did it go?

I'm hoping to install some of these, this weekend too
I also have an issue with warped rotors.

bikaholic

Sponginess in the lever feel (usually the rear brake) is affected by how you route the last third section of the brake outer cable and the order in which you clip/zip-tie/tape the cable outer onto the frame.

The optimum method is to have the levers and calipers connected up, with the inner cable under tension, before you clip/zip-tie/tape the cable outer to the frame. This applies to brake as well as gear cables for mtb and road components.

There will be less internal friction if the last third section of the brake outer cable is as straight as posible going into the rear caliper and thus the lever will feel smooth and light. If you temporarily zip-tie the cable outer to the frame (usually the left seatstay) so that it introduces an acute bend in the cable then sponginess in lever feel will increase. So, avoid acute bends in the last third of the cable outer, even if this means that you omit the use of the framestop (where a clip or zip-tie goes), if you want to improve lever feel.

bikaholic

You should employ the tradesman's method as opposed to the flatpack method (as in flatpack furniture assembly) when you come to install brakes with warped rotors.

Basically, you ignore Avid's tech doc instructions and do everything by eye because Avid's tech docs assume perfect conditions.

I've posted the generic installation method before and so won't repeat them here again. It has been tested since 1999 so the method definitely works.

Danny523

r3hxn wrote:

how did it go?

I'm hoping to install some of these, this weekend too
I also have an issue with warped rotors.

I haven't actually tried truing them yet, but I managed to line the caliper up a bit better, I took it for a small ride around to try and bed them in, and they are definitely getting better already after half an hour of riding, so I'm feeling hopeful!